I used to stress over measurements and how to measure up before starting. If time and a lot of mistakes have taught me anything, let the bow just become a bow and throw away the calipers and tape measure. Sure different woods lend themselves to different widths, but only experience of failure can really teach you anything.
Go cut a sapling down and just experiment. You will soon figure out for yourself what works and what does not. Keeping it minimal might take you long time to improve but if I can share anything that I have learned, my advice would be, just build bows until you get what works for you.
Dean